Radiant heating devices



May 23, 1967 A. VEZZOLI RADIANT HEATING DEVICES Filed July 12, 1965 INVEIV'TOR Lows ALI X VE'ZZOL BY ATTORN Y United States Patent Claims. (a. 158-130) The present invention relates to a safety device against back-firing in radiant gas burners.

This back-firing phenomenon in gas burners is known, which consists of a shiftig of the combustion zone upstream from its normal position, that is to say towards the origin of the fuel mixture feed: the injector in general.

This phenomenon, caused by numerous accidental factors, such as too great an increase in fuel flow, alteration in the feed-in of air, breakage or alterations in the cross section of the flame outlet or outlets, is harmful as it sometimes causes explosions, or deteriorations of the burner, as well as accidents due to the considerable leakage of gas after abnormal heating of the taps or the feed system.

The phenomenon is generally progressive, the flame surface taking a certain time to go upstream of the flame outlet aperture, generally under the influence of parameters which are independent of the burner construction. It may become almost instantaneous when a part of the burner breaks, especially at the flame outlet section.

In the case of radiant burners, the flame surface or combustion zone is stabilized near the outer surface of refractory plates of a certain thickness which are pierced of a multiplicity of passages for distributing the combustible mixture on the said outer surface, while maintaining, in normal use, the inner surface at a temperature lower than the ignition temperature of the said mixture. Therefore, there establishes a temperature gradient throughout the thickness of the plate and the temperature at inner points of the plate, or that at its outer surface has a tendency to rise considerably as the back-firing occurs; a radiant burner is the more sensitive to backfiring the smaller the thickness of the refractory plate, if it is made of a material which is a more heat conductive or if the apertures of the through passages are larger.

It has been found that the above mentioned drawbacks could be avoided, and the safety and operational regularity of radiant burners thus increased, by sensitizing an area of the radiant surface in order to enable the formation of a localized or limited back-firing before conditions causing a general back-firing are established on the whole of the radiant surface, all provisions being made to avoid the development of the said local back-firing into a general back-firing by using the said local back-firing to cut off the supply of fuel to the burner.

In practice, the invention enables the formation of bacl -firing conditions in the said zone to be detected and to cause the said detection to take effect on the burner feed in time.

Another object of the invention is to provide a device for utilizing this safety method, the said device making it possible to detect the start of a back-firing and to cut off the arrival of fuel in the burner before the phenomenon occurs in its entirety, with all the consequences involved.

A device according to the invention a detection chamber formed in an area located behind the radiant surface, a spring biased electrovalve controlling the arrival of fuel and two thermocouples mounted in opposition in series with the electrovalve controlwinding, the first being housed in the detection chamber and comprises primarily 3,321,001 Patented May 23, 1967 the second mounted in front of and adjacent to the radiant surface, in such a manner that when the burner is normally fed and a back-firing starts to occur in the detection chamber, the first thermocouple progressively bucks the current supplied by the second and thus causes the electrovalve to close through the action of the spring bias. Under these conditions the detection chamber constitutes a point, or zone, of preferential firing protected on the feeding side in such a manner that it does not act as a bypass for a general back-firing before the anti backfiring thermocouple has cut off the fuel supply by means of the electrovalve.

The detection chamber may be incorporated in the radiant plate itself or be formed behind the same.

The walls of the detection chamber may consist entirely of plates of the same kind as the plate or plates forming the radiant panel.

The detection chamber may also have a front wall consisting of a plate having the same nature and characteristics as the plate or plates forming the radiant panel, or have a front wall formed of a material which is a better heat conductor than the radiant plate or plates.

The invention is described in greater detail hereinafter, with reference to the appended drawings in which:

FIG. 1 is a diagrammatic sectional view of a preferred embodiment of the invention.

FIG. 2 is a similar view of a modified embodiment of the detection chamber.

As diagrammatically shown at FIGURE 1, the device according to the invention comprises a fuel inlet electrovalve 1 controlling a pipe 2 connected to a. flammable air and gas mixture supply system, such as a venturi 3 for instance, projecting the flammable mixture into a closed chamber 4, on wall of which is formed of a plate 5 of refractory material having a multiplicity of channels there through and which constitutes the burner. Electrovalve 1 comprises a spring (not shown) which urges said valve toward its closed position.

According to the invention, a housing 6 is formed in plate 5 by two small perforated plates 7 and 8 forming together a small chamber 9 in which is placed a thermocouple 10. Said thermocouple 10 is connected, on one hand to another thermocouple 11 placed before and adjacent to plate 5, and on the other hand to one of the terminals of the winding 12 of electrovalve 1, the other terminal of which is connected to the second thermocouple 11. The two thermocouples 10 and 11 are mounted in opposition, i.e. the positive terminals thereof are coupled together whereas their negative terminals are connected to the respective terminals of winding 12.

The device operates as follows.

The fuel supply electrovalve 1 is held open by the current from thermocouple 11, placed before the radiating surface of the burner and which operates as a safety device in case of extinction.

The flammable mixtures from chamber 4 passes through the channels in plate 5 and in the small plates 7 and 8 to burn in the vicinity of the outer surface of the burner.

The privileged plate 7, consisting of a small identical in form and nature to plate 5, is less thick than the latter, whereby as the flames move back into the plate assembly the ignition temperature of the flammable mixture is reached on the rear surface of small plate 7 before it is reached on the rear surface of plate 5. Therefore ignition of the flammable mixture occurs in the small detection chamber 0 but is not immediatedly communicated to the whole of the general mixing chamber 4 due to the small plate "8 closing said chamber 9. Owing to this ignition thermocouple 10 is heated and generates an increasing electric current, the value of which rapidly reaches that of the current generated by thermocouple 111, the current in the circuit of winding 12 is thereby annulled, electrovalve 1 is no longer supplied with current and the bias spring thereof caused it to close.

From the moment when the mixture has ignited in chamber 9, the response time is practically null and enables the fuel feed to be cut off well before the temperature has reached a dangerous value on the rear side of the plates or before the flame has time to pass through plate 8. V

The invention is of course not limited to the above described preferred embodiment. It is also possible, as shown in FIGURE 2, to constitute a privileged plate by a cutting out part ofplate 5 of the burner and inserting therein a small plate 7' of the same nature and thickness as said plate 5, but having channels of a slightly greater diameter than the channels in plate 5. A chamber 9' is then formed on the rear face of plate 7 which is closed by a small perforated plate 8' and within which is arranged thermocouple 10.

The privileged plate may also, in this case, be designed in a geometrically identical manner to the other plate or plates forming the heating pannel, but of a material which is a better heat conductor.

I claim:

1. In a gas radiant burner comprising a radiant burner plate having a multiplicity of narrow passages extending therethrough from a rear surface of said block to a front surface thereof for conducting from said rear surface to said front surface streams of a flammable gas mixture for combustion adjacent said front surface, and means for feeding said flammable gas mixture to said rear surface of said plate, including a fuel feed duct: 21 detecting chamber provided behind said front surface and separated therefrom by a perforated radiant plate element which is more sensitive to back-firing than said radiant burner plate, anti-back-firing means for feeding said flammable gas mixture to said detecting chamber, a self closing electrovalve on said fuel feed duct, a solenoid for controlling said electrovalve to an open position when energized, said solenoid having two terminals, a first thermocouple arranged in front of and adjacent to said front surface of said radiant burner plate, a second thermocouple arranged within said detection chamber, said first and second thermocouples being coupled in opposition to one another and in series with said terminals of said solenoid, whereby said first thermocouple generates a first current for energizing said solenoid to open said electrovalve upon said combustion of said flammable gas mixture adjacent said front surface of said radiant burner plate and said second thermocouple generates a second current which annuls said first current when back-firing occurs in said detection chamber.

2. In a gas radiant burner comprising a radiant burner plate having a multiplicity of narrow passages extending therethrough from a rear surface of said block to a front surface thereof for conducting from said rear surface to said front surface streams of a flammable gas mixture for combustion adjacent said front surface, and means for feeding said flammable gas mixture to said rear sursurface of said plate, including a fuel feed duct: a detecting chamber out out within said radiant burner plate between said front surface and said rear surface, separated from said front surface by a section of said plate which is thinner than said plate, a self closing electrovalve on said fuel feed duct, a solenoid for controlling said electrovalve to an open position when energized, said solenoid having two terminals, a first thermocouple arranged in front of and adjacent to said front surface of said radiant burner plate, a second thermocouple arranged within said detection chamber, said first and second thermocouples being coupled in opposition to one another and in series with said terminals of said solenoid, whereby said first thermocouple generates a first current for energizing said solenoid to open said electrovalve upon said combustion of said flammable gas mixture adjacent said front surface of said radiant burner plate and said second thermocouple generates a second current which annuls said first current when back-firing occurs in said detection chamber.

3. In a gas radiant burner comprising a radian-t burner plate having a multiplicity of narrow passages extending therethrough from a rear surface of said block to a front surface thereof for conducting from said rear surface to said front surface streams of a flammable gas mixture for combustion adjacent said front surface, and means for feeding said flammable gas mixture to said rear surface of said plate, including a fuel feed duct: a detecting chamber provided behind a cut out section in said radiant burner plate, a perforated radiant plate element replacing said cut out section to close said detecting chamber, which is more sensitive to back-firing than said radiant burner plate, anti-back-firing means for feeding said flammable gas mixture to said detecting chamber, a selfclosing electrovalve on said fuel feed duct, a solenoid for controlling said electrovalve to an open position when energized, said solenoid having two terminals, a first thermocouple arranged in front of and adjacent to said front surface of said radiant burner plate, a second thermocouple arranged within said detection chamber, said first and second thermocouples being coupled in opposition to one another and in series with said terminals of said solenoid, whereby said first thermocouple generates a first current for energizing said solenoid to open said electrovalve upon said combustion of said flammable gas mixture adjacent said front surface of said radian-t burner plate and said second thermocouple generates a second current which annuls said first current when back-firing occurs in said detection chamber.

4. A burner as claimed in claim 3, in which said perforated radiant plate element closing said detection chamber has passages therethrough having a larger cross section than the passages in said radiant burner plate.

5. A burner as claimed in claim 3, in which said perforated radiant plate element closing said detection chamber is made of a material having a lower heat conductivity than said radiant burner plate.

References Cited by the Examiner UNITED STATES PATENTS 2,285,866 6/1942 Markle.

FREDERICK KETTERER, Primary Examiner. 

1. IN A GAS RADIANT BURNER COMPRISING A RADIANT BURNER PLATE HAVING A MULTIPLICITY OF NARROW PASSAGES EXTENDING THERETHROUGH FROM A REAR SURFACE OF SAID BLOCK TO A FRONT SURFACE THEREOF FOR CONDUCTING FROM SAID REAR SURFACE TO SAID FRONT SURFACE STREAMS OF A FLAMMABLE GAS MIXTURE FOR COMBUSTION ADJACENT SAID FRONT SURFACE, AND MEANS FOR FEEDING SAID FLAMMABLE GAS MIXTURE TO SAID REAR SURFACE OF SAID PLATE, INCLUDING A FUEL FEED DUCT: A DETECTING CHAMBER PROVIDED BEHIND SAID FRONT SURFACE AND SEPARATE THEREFROM BY A PERFORATED RADIANT PLATE ELEMENT WHICH IS MORE SENSITIVE TO BACK-FIRING THAN SAID RADIANT BURNER PLATE, ANTI-BACK-FIRING MEANS FOR FEEDING SAID FLAMMABLE GAS MIXTURE TO SAID DETECTING CHAMBER, A SELF CLOSING ELECTROVALVE ON SAID FUEL DUCT, A SOLENOID FOR CONTROLLING SAID ELECTROVALVE TO AN OPEN POSITION WHEN ENERGIZED, SAID SOLENOID HAVING TWO TERMINALS, A FIRST THERMOCOUPLE ARRANGED IN FRONT OF AND ADJACENT TO SAID FRONT SURFACE OF SAID RADIANT BURNER PLATE, A SECOND THERMOCOUPLE ARRANGED WITHIN SAID DETECTION CHAMBER, SAID FIRST AND SECOND THERMOCOUPLES BEING COUPLED IN OPPOSITION TO ONE ANOTHER AND IN SERIES WITH SAID TERMINALS OF SAID SOLENOID, WHEREBY SAID FIRST THERMOCOUPLE GENERATES A FIRST CURRENT FOR ENERGIZING SAID SOLENOID TO OPEN SAID ELECTROVALVE UPON SAID COMBUSTION OF SAID FLAMMABLE GAS MIXTURE ADJACENT SAID FRONT SURFACE OF SAID RADIANT BURNER PLATE AND SAID SECOND THERMOCOUPLE GENERATES A SECOND CURRENT WHICH ANNULS SAID FIRST CURRENT WHEN BACK-FIRING OCCURS IN SAID DETECTION CHAMBER. 